An electrophotographic copier or printer has a seal member made of fiber sealing a portion of a rotation shaft of a powder carrier so as not to allow powder to leak from the portion of the rotation shaft of the carrier of micro-powder such as toner. When such a powder carrier is used, fiber falls off from an end of the seal member (hereinafter, the falling off of fiber is referred to as “fiber-falloff”). Conventionally, to take measures for the fiber-falloff, a back face of a foundation cloth made of ground yarn supporting the fabric of the seal member is subjected to a coating process with a coating agent, i.e., a backing process with a backing agent to prevent the fiber-falloff. However, recently, as powder used are further reduced in size, ultra-fine fiber thinner than conventional fiber is increasingly used as the fiber used for the seal member. The method of taking measures for the fiber-falloff using a coating, i.e., backing (hereinafter referred to as “coating”) process executed for conventional fiber does not sufficiently prevent the fiber-falloff since the fiber-falloff occurs from a cutting end portion when a seal member made of the ultra-fine fiber is cut into a predetermined shape as a seal member. Therefore, this leads to the occurrence of a phenomenon that the fiber-falloff does not stop even if the seal member made of the ultra-fine fiber is subjected to predetermined cleaning in advance before use. With regard to a thickness of fiber making up a pile used for the seal member, ultra-fine continuous fiber having a diameter equal to or less than 3 deniers, i.e., 20 μm is recently increasingly used for sealing micro-powder of several microns. However, even the pile yarn using this ultra-fine continuous fiber leads to the notable occurrence of the phenomenon that the fiber-falloff does not stop.
In consideration of the sealing property of the seal member, ultra-fine fiber is recently used in, for example, an image forming apparatus and a copier forming an image in an electrophotographic mode, so as to prevent leakage of toner, which is powder, from the root of the seal member. Since the ultra-fine fiber or the pile yarn spun from the ultra-fine fiber is used for preventing the toner leakage, it increasingly becomes difficult to open the root of the ultra-fine fiber or to open the root of the pile yarn spun from the ultra-fine fiber. Additionally, since a viscous coating agent, i.e., backing agent, (hereinafter referred to as “coating agent”) is applied from the back face of the seal member, the applied coating agent infiltrates into pile yarn from a foundation cloth made of ground yarn due to a capillary phenomenon between pieces of fiber and infiltrates into the fiber to a height having an effect on the sealing property. As a result, the solidification of the root of the pile yarn due to the coating agent causes many voids in the root of the pile yarn and deteriorates the sealing property in the root of the pile yarn, resulting in toner leakage from the root of the pile yarn. Therefore, a seal member including crimping fiber in pile yarn has been proposed for taking measures against the toner leakage from the root of the pile yarn (see, e.g., Patent Document 1). However, even in this proposal, the pile yarn including ultra-fine fiber causes higher infiltration of the coating agent into the pile yarn, thereby reducing the expected effect by half.
A proposal has also been made on a seal member that has a certain degree of thickness, that exhibits a proper sealing property, and that can be manufactured without a complicated manufacturing process with reduced manufacturing cost (see, e.g., Patent Document 2). Specifically, the seal member is made of a pile fabric, in which a thickness of a foundation cloth made of ground yarn is 1.0 to 5.0 mm, and the density of pile yarn in the pile fabric is equal to or greater than 60 pieces/mm2. Since the seal member can be manufactured without undergoing a bonding process of a cushion layer on the back side of the seal member as in the conventional case, the seal member eliminates concerns about crushing of the pile yarn occurring due to the bonding. However, more improvements are required in the sealing property and the manufacturability of the seal member for powder using ultra-fine fiber even in this case.